For a substantial period of time, various air inlet means have been provided in the cabs and bodies of vehicles of various kinds for purposes of providing comfort to the occupants. Usually, the air entrance opening was covered by a suitable screen to prevent the entrance of insects and other elements floating in the atmosphere which generally are larger than dust, whereby a screen mesh of reasonable size, such as insect screening, was adequate to prevent entrance of such items into the interior of the enclosed cab or body of the vehicle. Typical examples of the aforementioned protecting screens associated with the air entrance openings are illustrated in U.S. Pat. Nos. 1,445,732 to Vondracek, dated Feb. 20, 1923; 1,621,770 to Eckland, dated Mar. 22, 1927; and 2,172,939 to Lintern et al, dated Sept. 12, 1939.
Especially for use in dusty atmospheres such as harvest fields, as well as manufacturing plants where dust is preuelant, more refined means have been utilized to prevent the entrance of dust to an enclosed cab of the vehicle. For use with the cab of a combine, one example of such more refined filter means is shown in U.S. Pat. No. 3,844,202 to Ferguson, dated Oct. 29, 1974, in which a pair of upstanding tubes having inlet means at the upper ends, surrounded by cylindrical filter elements, are used to filter the entrance of air to the interior of the cab of a combine.
One further refined version of a filter element for the cab of a tractor, for example, is shown in U.S. Pat. No. 3,868,896 to Doll et al, dated Mar. 4, 1975, in which filter means are provided on the interior of a roof of a cab of a tractor, the air entering the cab through a block-type filter element which is supported over an inlet opening by clamping means, said inlet being exterior of the cab adjacent the rear window thereof, but when the filter is to be replaced or cleaned, the element which has dust and dirt adhering thereto and clogged in the pores thereof, must be removed into the interior of the cab, thereby permitting dust and dirt to fall into the interior and thus defeat some of the object of utilizing the filter.
The filter arrangement comprising the present invention is arranged so that the entire filter, including means to remove and replace the same, are exterior of the cab under all circumstances and are relatively simple to construct and operate.